A Method of Molding a Peripherally Encapsulated Product Under Heat and Pressure Utilizing Sheet Molding Compound (SMC) or Bulk Molding Compound (BMC), and
The Peripherally Encapsulated Product
It is conventional to insert a small panel or piece of glass into a cavity of a multi-part mold and inject therein under elevated temperature and pressure polymeric/copolymeric material which peripherally encapsulates a peripheral edge of the glass. An early injection molding system of this type was used, for example, to manufacture lens mounts, as disclosed in U.S. Pat. No. 2,266,169 in the name of Chester W. Crumrine which granted on Dec. 16, 1941. A lens element is clamped between two centering plungers which hold the lens with a peripheral edge thereof projecting into an annular cavity into which hot plastic is injected under pressure, cools and is subsequently removed from the mold cavity in the form of a lens mount. Similar injection molding to form peripherally encapsulated pieces of glass are found in U.S. Pat. Nos. 2,559,860 and 3,971,841 issued to Howard G. Fay and Leon Rubinstein, respectively, on Jul. 10, 1951 and Jul. 27, 1976, respectively. Each of these two patents relate to lens systems for photographic apparatus.
Larger pieces of glass have also been similarly provided with an injection molded rim, encapsulation, or frame, as in U.S. Pat. Nos. 4,626,185; 4,695,420 and 5,676,894 in the respective names of Bernard Monnet, Charles E. Grawey et al. and Paul Specht, which issued respectively on Dec. 2, 1986; Sep. 2, 1987 and Oct. 14, 1997. Such larger encapsulated glass structures are typically used as curved automobile glass panels, printed circuit boards, window panes, structural paneling, and the like.
Another approach toward the manufacture of a frame member which encapsulates a peripheral edge of a panel is found in U.S. Pat. No. 5,329,686 in the name of Maurice A. Kildal et al. issued on Jul. 19, 1994. In this patent a panel is placed between a frame member with an edge thereof being located in a recess while an integral lip of the frame member can be bent a distance sufficient to allow the panel to be peripherally clamped to the frame. Heretofore eye glass rims were so constructed, as is evidenced by U.S. Pat. No. 3,399,018 in the name of Conrad L. Leblanc issued on Aug. 27, 1968.
Well prior to the latter disclosures, powdered material was placed in an annular cavity of a mold into which was inserted a piece of tempered glass, and upon the closing of the mold with the glass clamped and centered therein, the powdered material melted and fused to a periphery of the glass. Typical of this process was the utilization of xe2x80x9cBakelitexe2x80x9d powder in the manner disclosed in U.S. Pat. No. 2,137,472 granted to Lewis Jex-Blake Forbes on Nov. 22, 1938.
In lieu of powder which can be molded under heat and pressure, as defined in the aforementioned patent, it had been common for years to utilize a ring or ring-like member of elastomeric material to form a seal for bearings or the like by placing the elastomeric member and a metal reinforcing member in a mold and closing the same under heat and pressure, as disclosed in U.S. Pat. No. 3,341,647 granted on Sep. 12, 1967 to Douglas J. Aberle. The seal is extruded about an inner periphery of the reinforcing member and is appropriately contoured to provide dual-lip seals with excess material being squeezed radially outwardly into a cavity for collecting excess unwanted elastomer.
Somewhat similar to the latter process is that of manufacturing such items as loudspeaker diaphragms between a pair of mating molds by inserting therein the diaphragm and, adjacent an edge thereof, a strip-shaped base material consisting of rubber as a main composition with an associated foaming agent. During heat and pressure molding in the cavity of the close mold the rubber is vulcanized and defines a foamed edge self-adhered to the outer periphery of the diaphragm, as disclosed in U.S. Pat. No. 5,705,108 issued Jan. 6, 1998 to A. Nonogaki.
The assignee of the present invention has expertise in the injection molded encapsulation of tempered glass which is used primarily for shelving, particularly for refrigerators, as is evidenced by U.S. Pat. Nos. 5,273,354; 5,362,145; 5,403,084; 5,429,433; 5,441,338 and 5,454,638 issued respectively on Dec. 28, 1993; Nov. 8, 1994; Apr. 4, 1995; Jul. 4, 1995; Aug. 15, 1995 and Oct. 3, 1995, all assigned to the assignee of the present application.
Typically, such encapsulated shelves are manufactured in an injection mold of the type disclosed in pending application Ser. No. 08/303,200 filed on Sep. 8, 1994 in the names of Max Meier et al. In the latter disclosure a tempered glass plate or panel has its peripheral edge located in a peripheral or annular cavity into which highly pressurized, hot, synthetic plastic polymeric/copolymeric material is injected and, upon subsequent cooling, the peripheral edge of the panel is bounded by a polymeric frame, rim or encapsulation which, since intended for use as a refrigerator shelf, has also integrally unitized thereto during molding opposite metallic shelf brackets.
A cooktop can be manufactured in much the same manner as that described immediately above, and a full disclosure thereof is found in commonly assigned pending U.S. application Ser. No. 08/890,651 filed on Jul. 9, 1997.
In keeping with the foregoing, a primary object of the present invention is to provide a novel and unobvious method of manufacturing a peripherally encapsulated unit, such as a range oven door, which in use is subject to relatively high temperatures, particularly when an oven is being automatically cleaned under elevated temperatures. Range oven doors are presently manufactured from metal which has a high degree of rigidity and temperature stability, resist distortion, can withstand abuse, etc. However, conventional range oven doors are made of many different pieces requiring separate formation, fabrication and assembly. Most commonly, such conventional range oven doors include a multipiece, inner, metal door frame assembly and a multipiece, oven door outer shell assembly. The latter are individually manufactured to include an oven door inner metal frame and an oven door outer shell, each of which has a tempered glass viewing panel or window. A separate metallic connecting flange through which fasteners pass is utilized for securing each glass panel to its associated frame and/or shell. The outer shell is also necessarily primed and painted to match or complement the color of the range/oven. All of this is extremely time consuming and costly.
The prior art patents referenced earlier herein suggest the manufacture of a range oven door by injection molding polymeric/copolymeric material under heat and pressure to encapsulate a peripheral edge of a tempered glass sheet. Unfortunately, the polymeric/copolymeric plastic materials available for injection molding cannot maintain tolerances, particularly if heated to relatively high temperatures. In other words, such materials generally lack relatively high hot rigidity at temperatures associated with baking, and even under relatively low temperatures the strength to weight ratio is relatively low i.e., the polymeric material is relatively weak and lacks the necessary strength, toughness and rigidity to withstand normal range oven door usage. Furthermore, while smaller products can be formed by injection molding polymeric material about the edge of a piece of glass, larger products create additional manufacturing problems, such as the control, reduction or elimination of product shrinkage. Absent non-shrink or low-shrink characteristics, it would be essentially impractical, if not impossible, to form an injection molded encapsulated polymeric/copolymeric oven door, be it an oven door outer shell or an oven door inner frame or both and connect the two together with repetitive accuracy. The individual shrinkage of each and the effects thereof one upon the other would essentially preclude either (a) inner and outer encapsulated units from being matchingly connected together or (b) either such encapsulated units from being matchingly connected to its multipart metal counterpart to form a commercially acceptable range oven door.
With the foregoing in mind, applicants have provided herewith a novel and unobvious method of molding a relatively large peripherally encapsulated product, such as a range oven door and specifically an oven door outer shell thereof by placing a piece of tempered glass between mold clamping portions of mold bodies when the latter are in an open position. One and preferably both of the mold bodies are heated and thermosetting polymeric material in the form of sheet molding compound (SMC) or bulk molding compound (BMC) is positioned upon one of the heated mold bodies within and about an area corresponding to an annular or peripheral mold cavity or chamber and outboard of a substantially continuous peripheral edge of the piece of tempered glass. The mold bodies are then progressively closed to thereby create compression forces upon the SMC/BMC which extrude the thermosetting polymeric material into the annular chamber and into complete peripheral edge encapsulation of the continuous peripheral edge of the tempered glass, including opposite face surfaces and a peripheral edge surface therebetween. As the mold bodies close, surfaces thereof define peripheral seals which prevent the SMC/BMC from escaping the annular mold cavity and instead the SMC/BMC is subject to relatively high compression forces which assure that the mold cavity is completely and intimately filled. After curing the thermosetting polymeric material under such heat and pressure, the mold bodies are opened and the peripherally encapsulated product is removed.
The steps of the method just described, when performed in conjunction with the proper weight and distribution of the thermosetting polymeric material (SMC/BMC) upon the associated mold body, assures the molding of a relatively dense, strong, tough and smooth-surfaced product essentially absent discernable flash, flash material, mold parting lines, voids, etc. Furthermore, since SMC/BMC can be effectively xe2x80x9cnon-shrinkxe2x80x9d compositions, as set forth in U.S. Pat. No. 3,947,615, the end product can be readily molded to exacting specifications and can readily fulfil its function, preferably as an oven door outer shell of an oven range door, for example.
In further accordance with the molding method of this invention, the annular mold cavity or chamber is contoured to impart to the oven door outer shell an annular front wall bounding the panel of tempered glass and being integrally united thereto under the heat and pressure of the xe2x80x9cextrudedxe2x80x9d SMC/BMC thermosetting material, while simultaneous therewith a flange-forming chamber portion of the annular mold cavity is likewise filled with the xe2x80x9cextrudatexe2x80x9d under heat and pressure to form an integrally molded peripheral flange. Additionally, the mold cavity is contoured to provide reinforced fastener-receiving bosses and reinforcing ribs at corners of the oven door outer shell.
In further keeping with the present invention, during the closing of the annular mold chamber, opposing surfaces of the flange-forming mold cavity portion thereof meet and form a xe2x80x9cslidingxe2x80x9d outer peripheral seal which prevents the polymeric material from being xe2x80x9cextrudedxe2x80x9d beyond the annular mold cavity under high molding pressures thus resulting in a relatively dense, smooth-surfaced, accurately dimensioned product.
The molded oven door outer shell constructed in accordance with the process of this invention is thus defined by a single piece of hot molded integral thermosetting polymeric material, such as SMC or BMC, forming a generally polygonal frame member defined by a front wall of a substantially annular configuration disposed substantially transverse to a peripheral wall or flange. The thermosetting polymeric molding compound has an inboardmost pressure xe2x80x9cextrudedxe2x80x9d peripheral edge portion which encapsulates a peripheral edge of a piece of tempered glass, including opposite peripheral face surfaces and a peripheral edge surface therebetween. This oven door outer shell, for example, can serve as a replacement for a conventional stainless steel oven door outer shell and can be united to the conventional inner steel frame by conventional fasteners threaded into the integrally molded reinforced fastener-receiving bosses at the corners of the polygonal frame member. The reinforcing ribs assure rigidity to the range oven door and/or the outer shell thereof over an extended lifetime of use.
With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings.